Neuroanatomical studies for immunocytochemical localization of a vasopressin-neurosecretory pathway will describe: sites of origin, its course to limbic system structures, and its probable termination on limbic system neuronal perikarya. In order to improve visualization of all elements of this pathway, immunocytochemistry for vasopressin (VP) will be performed on serial-sectioned brains of animals administered colchicine and ethanol. Lesioning possible sites of origin of this pathway, followed by immuno-staining for VP associated with target neurons, should indicate which neurosecretory cell groups contribute nerve terminals to limbic system structures; then, immunoelectron microscopy will be used to discern the VP-containing terminals. The target neurons for this pathway will be examined by their autoradiographic ability to bind radiolabeled VP, and their mediation of behavioral effects in the absence of VP. Behavioral testing will be conducted in animals following stereotactic injections of VP into limbic sites which have lost their vasopressinergic innervation due to specific lesioning of VP-cell groups thought to project to these sites and, also, after both regional and intraventricular injections of anti-VP which should differentiate between a local or general action of VP on limbic system function. Finally, results of behavioral tasks should determine whether VP alters the animal's perception of the significance of stimuli. Thus, our objectives are to elucidate the anatomical components of a VP-containing pathway which provide input to certain structures of the limbic system and to test whether VP is a causative agent for behavioral functions of these same limbic structures.